1. Field of the Invention
The present invention pertains to towed array marine seismic surveying.
2. Description of Related Art
The exercise of examining subterranean geological formations for deposits of hydrocarbon deposits is known as “seismic surveying”. Sometimes the geological formations lie beneath a body of water. This type of seismic survey is known as a “marine” seismic survey. Marine seismic surveys may be performed in salt, fresh, or brackish waters and are not limited to saltwater environments.
One type of marine seismic survey is called a “towed-array” seismic survey. In such a survey, a tow vessel tows an array of equipment along a sail line. The array usually includes a number of seismic streamers, typically up to eight of them, each up to several kilometers long. The streamers are populated with a number of instruments, most notably seismic receivers such as hydrophones and sometimes particle motion sensors. Sometimes the array will also include a plurality of seismic sources. As the array is towed, the streamers ideally straighten and roughly parallel each other. Sometimes environmental or survey conditions adversely impact the shape of the array, but this is the ideal shape.
Towed-array seismic survey spreads therefore include control systems to control the position of various elements in the spread. Some of these elements are used for data acquisition. But others are used for the express purpose of positioning some portion of the spread, thereby controlling the shape of the spread and, hence, the position of the acquisition elements.